Typically, a raw gas stream to be filtered by the hot gas filtration system enters the filter vessel via said raw gas inlet, passes through said plurality of filter elements while contaminants comprised in the raw gas stream are collected on the upstream surface of the raw gas portions of the filter elements. Clean gas exits the filter elements at their clean gas ends, enters into the clean gas section, and a clean gas stream is discharged from the vessel via said clean gas outlet.
From time to time, the contaminants collected at the upstream side of the filter elements are removed therefrom by a blowback gas pulse generated by said blowback arrangement in a regeneration process. The detached contaminants are collected and discharged from the raw gas section of the filter vessel. The long-term performance of the hot gas filtration system crucially depends on the effectiveness of the regeneration process. Regeneration of the filter elements may be hindered by formation of bridges of contaminants between the upstream surfaces of adjacent filter elements increasing the risk of failure or breakage of the filter elements.
Hot gas filtration systems of the afore-described type often require huge dimensions. A filter vessel may very well have a diameter of about 4 m, a height of about 14 in and accommodate 1000 filter elements or more.
Typically, filter elements are made of a ceramic material and have a length of about 1.5 to 2.5 m and an outer diameter of about 60 mm. Alternatively, the filter elements may be made of metal. Such filter elements may have an even greater length. An exemplary filter vessel including the tubesheet and the filter elements may have a weight of roughly 100 metric tons.
In the hot gas filtration system according to U.S. Pat. No. 5,143,530, the particuate matter is deposited on the exterior (upstream) surface of a plurality of filter candle type filter elements. The plurality of filter elements is divided into a number of groups of filter elements. The clean gas ends of the filter elements of each group are connected to separate filtrate chambers which are in fluid communication with a clean gas outlet. During the regeneration process, a cleaning gas pulse is introduced into a blowback supply line and split into a number of cleaning gas streams corresponding to the number of groups of filter elements and filtrate chambers.
U.S. Pat. No. 5,752,999 suggests a hot gas filtration system where, in contrast to U.S. Pat. No. 5,143,530, raw gas is fed into the interior of filter candles, so that particulate matter comprised in the raw gas accumulates within the filter elements, thereby avoiding the formation of bridges of particulate contaminants between adjacent filter elements. In order to regenerate the filter elements, a pulse of clean gas is injected to discharge the accumulated particulate matter from within the filter elements. The plurality of filter elements is divided into several groups of filter elements, each group being accommodated in a plenum chamber.
Since the plenum chamber accommodates the whole of the filter elements, such concept significantly increases the manufacturing costs.
In addition, the use of the inner surface of the filter candles instead of the outer surface for collecting the contaminants comprised in the raw gas the available filtering (upstream) surface and, consequently, the filtration capacity of the system is substantially decreased. Therefore, the regeneration process has to be performed more frequently.
According to US patent application 2002/0014156 A1, the filter elements of a hot gas filtration system are provided at their clean gas ends with so-called safety fuses which provide additional safety in case of breakage of one of the filter elements. The filtration system further comprises a clean gas outlet with a closure element in the form of a flow-dynamic control element which blocks the clean gas outlet of the vessel automatically when a backflushing gas pulse is fed into the clean gas section of the interior of the filter vessel. This filtration system makes use of high speed valves having very short switching times of about several 10 msec. The flow-dynamic control element inevitably presents a noticeable resistance to the flow of clean gas.